Electronic musical instrument



Dec. 16, 1969 Filed March 28, 19?

D. R. MOORE ELECTRONIC MUS ICAL INSTRUMENT 2 Sheets-Sheet l @0f/@Ms EMO/P5,

I N VENT OR,

C@ BY f Dec. 16, 1969 D. R. MOORE ELECTRONIC MUSICAL INSTRUMENT 2 sheets-sheet z Filed March 28. 1967 @oz/@AAS A? /f/oo/@ZI` INVENTOR BY f rro/fwfy United States Patent O 3,484,529 ELECTRONIC MUSICAL INSTRUMENT Douglas R. Moore, Los Angeles, Calif., assignor to Rheem Manufacturing Company, New York,

l N.Y., a corporation of California Filed Mar. 28, 1967, Ser. No. 626,510 Int. Cl. Gh 1/02 U.S. Cl. 84--1.01 10 Claims ABSTRACT OF THE DISCLOSURE An electronic instrument for providing string-timbre tones comprising a single oscillator whose frequency is controlled by switching of a plurality of resistors into or out of the oscillator circuit. The output of the oscillator is supplied to a gate control circuit and thence to a Wave shaper and gate. The latter circuit provides at least two harmonics of the fundamental frequency generated by the oscillator.

One of the features of the invention is that if more than one of 24 possible keys is closed, only the key corresponding to the highest note will be effective and any other depressed key will be ineffective.

This invention relates to an electronic musical instrument for providing string-timbre tones that may serve as an adjunct to a piano or other instrument, or may be rused independently of any other instrument. It is particularly adapted for use as a bass adjunct with a stringed instrument and will be described in that context, although not limited thereto.

Various electronic musical instruments for providing string-timbre tones have `been proposed in the past. However, these instruments have generally suffered from one or more disadvantages. For example, many of them have required a separate electronic oscillator for each tone generated, which represents a considerable cost factor when it is considered that each oscillator requires two transistors. The cost was further increased by a requireyment for a separate iilter for each generated tone. In ad* dition, if two or more oscillators were energized at the same time, discordant sounds could well be produced. The cost of such instruments often ran into many lhundreds of dollars.

l The present invention eliminates the foregoing disadvantages by providing an instrument embodying a single oscillaton whose frequency of oscillation may be varied through a plurality of frequencies by switching one or more resistors into the oscillator circuit. A single iilter is used for all of the oscillator output tones, and no 'discordance can result.

` When any one (or more) keyboard or foot pedal switches is closed, the oscillator is energized through `a gate control circuit and oscillates at a frequency determined by the amount of resistance switched into the circuit by closing of the switch. The gate control circuit also turns on a wave Shaper and gate circuit when a switch energizes the gate control circuit. Means are provided in the gate control and wave Shaper and gate circuits for producing either arco (sustained) or pizzicato modes of operation, and also for varying the harmonic content of the output tones to stimulate either a cello or'double bass.

` The invention, together with further features and advantages thereof, will be better understood from the yfollowing description, taken in conjunction with the aoompanying drawings, in which:

, FIGURE l is a simplitied block diagram of an instrument embodying the invention;

Patented Dec. 16, 1969 FIGURE 2 is a schematic diagram of the instrument; and

FIGURE 3 is a group of waveforms useful in understanding the operation of the circuit.

The block diagram of FIGURE 1 shows a gate control circuit 10, which is controlled by one of a plurality of switch means shown generally by a block 12. In turn, the gate control circuit 10 controls a wave Shaper and gate circuit 16 that provides an output to a terminal 18. Whenever any one of the switch means 12 is closed, it turns on the oscillator 14, which oscillates at a frequency determined .by which of the switches is closed. The output of the oscillator 14, which is rsupplied to the wave Shaper and gate circuit 16, is essentially a pure sine wave. The wave Shaper serves to clip the sine wave to provide a square wave containing harmonics to provide various output timbres. As previously mentioned, either an -arco or pizzicato effect can be obtained and the harmonic content of the output signal can simulate either a cello or double bass. Of course, other controls are provided to vary overall tuning of the oscillator 14 and the volume of the output signals from the wave shaper and gate 16.

In the circuit diagram shown in FIGURE 2, a potential +V is provided to a terminal 20 connected to a potential supply line 22 which energizes the entire circuit. The gate control circuit 10 comprises a pair of NPN transistors 24 and 26. The switches 12 shown in block form in FIGURE 1 include switches 30-76. Theoscillator 14 comprises two NPN transistors 80 and 82, and the wave shaper and gate 16 includes NPN transistors 84 and 86 and a synthesis filter including a transformer 88 having a center-tapped primary `winding 88a and a secondary Winding 88h.

The switches 30-76 are normally-open, single-pole, single-throw, spring-loaded switches having their poles connected to ground through a line 90. A plurality of impedances such as adjustable resistors 92-136 are respectively connected between the contacts of the switches Sil-'76. The end of the resistor 92 is connected to the supply line 22 through a variable resistor 138, a resistor 140, a resistor 142 and a resistor 144. The juncture of re sistors 142 and 144 is connected to ground through a capacitor 145. It is pointed out that if one of the switches is closed, for example, the switch 40, and another switch such as the switch 50 is also closed, closing of the switch Si) will have no effect. Only the switch corresponding to the higher note will be effective.

Looking at the gate control circuit 10 in detail, it is seen that the base of the transistor 24 is connected to the supply line 22 through the resistor 144, the col-lector of the transistor 24 is connected to the supply line 22 through a load resistor i146 and the emitter is grounded. Output is provided from the collector of the transistor 2-4 through `a resistor 148 to the base of the transistor 26 across a resistor 150 connecting the base of the transistor 26 to ground. The collector 4of the transistor 26 is connected to the supply line 22 through :a load resistor 152 Aand the emitter of the transistor 26 is grounded.

When none of the switches 30-76 is closed, the-base of the transistor 24 is forward -biased and the transistor 24 is conducting. Thus, the base of the transistor 26 is essentially at ground and that transistor is nonconducting. As will become apparent later, when all of the aforementioned switches are open and the transistor 24 is conducting, the oscillator 14 is inoperative and there is no output from the circuit. y,

Looking now at the oscillator 14, it is seen that the collector of the transistor is connected to supply line 22 through a resistor 154 and the collector of the transistor 82 is similarly connected through a resistor 156.k The collector of the transistor 80 is directly connected to the base of the transistor 82 and the emitter of the transistor 80 is grounded. The base of the transistor 80 is connected to ground th ough series resistors 158, 160, and 162, and the emit of the transistor 82 is connected to the juncture of the resistors 160 and 162. The resistors 158 and 160 are feedback resistors and, of course, the resistors 154 and 156 are load resistors. Capacitors 164 and 166 are connected in series between the base of the transistor 80 and the juncture of the resistors 160 and 162. Capacitors 168 and 170 are connected in series between the juncture of resistors 158 and 160 in ground, and a variable resistor 172 is connected across the capacitor 170. The variable resistor 172 serves Ias a tine tuning adjustment, which changes the oscillator range without changing the tone intervals.

The oscillator 14 is a modied twin T oscillator, whose frequency of oscillation is determined by a circuit comprising capacitors 164, 166, 168 and 170 `and by resistors 140, 172, 158, 160, 138 and 92-136. When any one of the resistors 92-136 is grounded, the oscillator is energized. The transistor 82 serves to isolate the output of the oscillator from the feedback components so that any loading will not change the oscillator frequency. The output of the oscillator is taken from the collector of the transistor 82 through a resistor 174 and capacitor 176 connected in series to the base of the transistor 84. The emitter of the transistor 84 is grounded and its collector is connected through an isolating resistor 178 to the center tap of the primary 88a of the synthesis filter transformer 88.

The lower end of the primary winding 88a is connected to ground through a capacitor 180 in parallel with series resistors 182 and i184, -with la switch 186 paralleling the resistor 184. The DC voltage existing across the capacitor 180 controls the amplitude of the instrument output signal when the oscillator 14 is energized.

The upper end of the primary winding 88a of the transformer 88 is connected through a capacitor 188 t-o the top of the capacitor 180 and to one end of a capacitor 190, whose other end is connected to the base of the transistor 84. A pair of capacitors 192 and 194 are connected in parallel across the capacitor 188 through manually operable, single-pole, single-throw switches 196 and 198, respectively. The capacitors 188, y192, 194 and switches 196 'and 198 are also part of the synthesis lter. The positions of the poles of the switches 196 and 198 control the resonant frequency of the filter and hence the timbre of the output signal. If the Switches 196 and 198 lare both open, the output signal represents a cello sound, which has the highest harmonic content of any signal available from the instrument of the invention. If the switches 196 and 198 are both closed, the output signal represents the sound of a double bass, which consists primarily of the fundamental and second harmonic of the fundamental and relatively little of the third harmonic.

Before looking at the output circuitry, consider the means for providing either arco (sustained) or pizzicato output tones. The choice of which output tone is obtained is made by the setting of a double-pole, d-ouble-position switch 200. When the switch is in the pizzicato position shown, the lanode of a diode 202 is connected to the collector of the transistor 26. The cathode of the diode 202 is connected to the top of the capacitor 180. A second diode 204 is connected in parallel with the diode 202, but with reverse polarity. In the pizzicato position of the switch 200, the cathode of the diode 204 is unconnected and, thus/that diode has no effect. When the poles of the switch 200 are moved to the left (as shown in the dr-awing)*to the arco position, both the cathode of the diode 204 and the anode of the diode 202 are connected to the collector of the transistor 24. The operation of the foregoing portion of the circuitry will be hereinafter described =withreference to'waveforms shown in FIGURE 3.

The top of the winding 8811 of the transformer 88 is connected .to the base of the transistor 86, and the bottom of the winding is connected to ground through a Capa itor 206 and to the supply line 22 through a resistor 208. The collector of the transistor 86 is connected directly to the supply line 22, and the emitter of the transistor is connected to ground through a resistor 210. A capacitor 212 and a potentiometer 214 are connected in Series across the resistor 210 and the output is taken from the movable arm of the potentiometer 214 and provided through a capacitor 216 to the output terminal 18. The capacitor 212, of course, blocks DC from the output and setting of the arm of the potentiometer 214 determines the amplitude of the output signals.

The operation of the instrument of the invention can -best be understood by referring both to FIGURES 2 yand 3. The curves A through G shown in FIGURE 3 correspond to the signals appearing at similarly designated points in the circuit diagram of FIGURE 2. The waveform A appears at the base of the transistor 24 inthe gate control circuitry 10. When all of the keys or switches 30-76 are open, the potential on the base of the transistor 24 is suicient to turn that transistor on. This, in turn, lowers the potential on the base of the transistors 26 and turns that transistor off. The waveforms D and E represent the signals on the collectors of the transistors 24 and 26.

When any one of the switches 30-76 is closed, a voltage divider is formed which lowers the potential on the base of the transistor 24 and turns that transistor off. This raises the potential on the base of the transistor 26 and turns that transistor on. As seen from waveforms D and E, the potentials on the collectors of the transistors 24 and 26, respectively, rise and fall. It is noted that resistor 142 is larger than the sum of resistor 140 and resistors 92-136 so that any loading at the base of the transistor 24 will not cause the oscillator 14 to function.

When a switch 30-76 is closed, the oscillator 14 comprising the transistors and 82 begins to function. Output of the oscillator is taken from the collector of the transistor 82 and is represented by the waveform B shown in FIGURE 3. The output of the oscillator is a fairly pure sine wave. In order to recreate a string musical sound, however, a predominance of certain harmonics are required.

As previously noted, the output of the oscillator is supplied to the base of the transistor 84. The desired harmonics are obtained by driving the transistor $4 beyond saturation so that the sine wave input from the transistor `82 is clipped as shown by waveform C representing the signal on the collector of the transistor 84. The square wave present on the collector of the transistor 84 contains the desired harmonics but not at the correct relative amplitudes. The adjustment of amplitudes is a function of the synthesis filter comprising the transformer 88 and the capacitors 188, 192 and 194. The lter is broadly resonant at the third harmonic of the center, or second, C provided by the instrument.

As previously mentioned, the instrument may be operated in either an arco or pizzicato mode. The mode is selected by the setting of the switch 200. In the arco mode, when the poles of the switch 200 are moved to the left from the position shown, the capacitor is connected to the collector of the transistor 24 through the diode 202. Inasmuch as when all switches 3076 are open, the transistor 24 is heavily conducting (as shown in Waveform D), the capacitor 180 will not be charged. The purpose of the diode 202 is to isolate the timing network from the gate control network so lthe timing will be determined entirely by the capacitor 180, resistors 18-2 and 184 and switch 186, and not by resistors 146 or 152. The rate at which the voltage across the capacitor 180 rises toward the supply voltage is determined by the value of the resistor 146. Generally, this imparts a slight delay time that causes the output tonel to swell to its desired amplitude and to maintain that amplitude until the switches 30-76 are all opened again. When the switches are opened, the signal at point D goes to ground and the capacitor 180 discharges. Its discharge path is through the resistor 182 and switch 186, and also through diode 4 and transist-or 24 which is now heavily conducting.

In the pizzicato mode of operation, the switch 200* is in the position shown. The capacitor 180 is connected through the diode 202 and the switch 200l to the collector of the transistor 26. Thus, before any one of the switches 30-76 is closed, the collector of the transistor 26 is essentially at the supply potential (waveform E) and the capacitor 180 is charged up to that level, as shown by the dashed curve in waveform F. When a key is closed, the capacitor 1-80 is prevented from discharging through the transistor 26 and must discharge through the resistors 182 and 184, or through the resistor 182 and the switch 186. Whether the switch 186 is open or closed determines which of two discharge rates the capacitor 180 will have. If the switch is closed, the discharge rate of the capacitor will, of course, be faster than if the switch is open. When the switches 30`76 are once again all opened, the capacitor 1-80 is recharged through the diode 202 as shown in waveform F. Waveform G is an idealized output waveform which shows that the arco output signal amplitude is dependent on the amplitude of the DC signal at point F. The transistor 84 is energized by a signal only when the oscillator 14 is functioning in response to one of the switches 30-76 being closed. The waveform G most closely resembles the output in the arco mode of operation. It is understood that in the pizzicato mode the signal would start at full amplitude and decay rapidly to zero. It is also pointed out that in the pizzicato mode the fundamental frequency decays more rapidly than the harmonic frequencies as is true in a stringed instrument.

It is now apparent that the instrument of the invention embodies a number of advantages not present in prior art devices. First, from the point of view of cost advantage, it eliminates the use of a separate oscillator for each tone to be generated and the use of a separate filter for each tone. A single oscillator and a single filter system are used for the generation of all tones. Second, only one set of switches is required to control the frequency of the oscillator and to provide a DC control voltage that initiates and terminates production of an output tone. Third, it eliminates any possibility of discordant output tones occurring, which has previously been possible when two or more keyboard switches are simultaneously closed.

It is apparent that many changes and modifications may be made to the musical instrument 0f the invention as disclosed in the single embodiment described herein without departing from the true spirit and scope of the invention.

What is claimed is:

1. An electronic musical instrument comprising:

potential supply means;

a plurality of variable impedances;

a plurality of first switch means for connecting selected ones of said plurality of impedances between said potential supply means and ground; and

a multi-staged transistorized oscillator having a circuit for determining frequency of oscillation, said circuit including a variable resistance coupling said oscillator to said plurality of impedances, grounding of different ones of said impedances varying said frequency of oscillation and energizing said oscillator.

2.'An electronic musical instrument comprising:

potential supply means;

a plurality of impedances;

a plurality of first switch means for connecting selected ones of said plurality of impedances between said potential supply means and ground;

an oscillator having a circuit for determining frequency of oscillation, said circuit including said plurality of impedances, grounding of different ones of said impedances varying said frequency of oscillation and energizing said oscillator; and

a gate circuit connected to said plurality of first switch means, a wave shaper circuit connected to said oscillator and to said gate circuit, and output circuitry connected to said wave Shaper circuit.

3. The instrument defined by claim 1, wherein said plurality of impedances comprise a plurality of impedances connected in series, and said first switch means are manually operable and are respectively connected between adjacent ones of said impedances and ground.

4. The instrument defined by claim 2, wherein said plurality of impedances comprise a plurality of impedances connected in series, and saidfirst switch means are manually operable and are respectively connected between adjacent ones of said impedances and ground.

5. The instrument dened `by claim 2, wherein said oscillator produces a sine wave output, and said wave circuit includes means from providing at least one harmonic of said sine wave output in the wave shaper output.

6. The instrument defined by claim 5, wherein said wave Shaper circuit contains means for selectively providing output signals representing tones having different timbres.

7. The instrument defined by claim 5, wherein said gate circuit contains second switch means for selectively providing sustained mode and pizzicato mode output tones from said wave shaper circuit.

8. The instrument defined by claim 7, wherein amplitude of said wave shaper output is controlled by a charge across capacitor means therein.

9. The instrument defined by claim 8, wherein in sustained mode, said capacitor means is charged through said second switch means While said oscillator is energized and discharged while said oscillator is de-energized.

10. The instrument defined by claim 8, wherein, in pizzicato mode, said capacitor means is charged through said second switch means while said oscillator is de-energized and discharged while said oscillator is energized.

References Cited UNITED STATES PATENTS 3,205,294 9/1965 Maynard 331-142 OTHER REFERENCES Maynard, F.: Twin-T Oscillators For Electronic Musical Instruments, In Electronics World, June 1964, pp. 36-39 and 79.

H. K. SAALBACH, Primary Examiner L. ALLAHUT, Assistant Examiner 

